Environmental Research with Lasers

The last examples illustrate that the most effective method of isotope separation is a combination of isotope-selective excitation with selective chemical reactions. The laser plays the role of an isotope-selective initiator of the chemical reactions [15.61]. 

The main advantages of laser applications in chemistry may be summarized 

More aspects of laser chemistry and many more examples of applications 

A detailed understanding of our environment, such as the earth s atmosphere, the water resources, and the soil, is of fundamental importance for mankind. 

A detailed understanding of our environment, such as the earth s atmosphere, the water resources, and the soil, is of fundamental importance for mankind. Since in densely populated industrial areas air and water pollution has become a serious problem, the study of pollutants and their reactions with natural components of our environment is urgently needed [1448], Various techniques of laser spectroscopy have been successfully employed in atmospheric and environmental research direct 

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The Nickel Producers Environmental Research Association (NiPERA) is sponsoring research on the application of inductively coupled plasma-mass spectroscopy (ICP-MS) to isotopic analysis of nickel in biological samples, on the development of sampling instrumentation for assessing workers exposure to nickel in the nickel industry, and on methods for utilizing newly developed analytical methods, such as laser beam ionization mass spectrometry, for the identification and speciation of nickel compounds in powders and dusts with particular reference to nickel refining. 

A convenient way to investigate the elemental and isotopic composition of the upper surface layers of small bodies of the Solar system is to use small-size laser mass spectrometers, mounted on a lander. Optimal for the purpose is a reflectron type time-of-flight mass analyzer with laser evaporation and ionization of the target, called LASMA (LASer Mass Analyser). It was created on the basis of a laboratory prototype, initially developed for the LIMA-D laser mass spectrometric system on the PHOBOS experiment, a space mission to the Mars satellite. A spin-off modification of the LASMA device was further developed for the special purposes of environmental research. 

The chip laser is actually a miniaturised version of the Nd-YAG laser. It contains a diode laser pump, an active laser medium, a saturable absorber, and a frequency multiplier in a solid block. Chip lasers are an inexpensive and reliable source of UV radiation. Unfortunately they cannot be made with repetition rates higher than a few tens of kHz. The pulse width is of the order of 1 ns. Chip lasers are sometimes used in TCSPC systems for environmental research, e.g. to trace contamination of water by polycyclic hydrocarbons. 

In the previous chapter we have seen how tunable lasers can be used in a multitude of ways to gain basic information on atomic and molecular systems. Thus, the laser has had a considerable impact on basic research, and its utility within the applied spectroscopic field is not smaller. We shall here discuss some applications of considerable interest. Previously, we have mainly chosen atomic spectroscopic examples rather than molecular ones, but in this chapter we shall mainly discuss applied molecular spectroscopy. First we will describe diagnostics of combustion processes and then discuss atmospheric monitoring by laser techniques. Different aspects of laser-induced fluorescence in liquids and solids will be considered with examples from the environmental, industrial and medical fields. We will also describe laser-induced chemical processes and isotope separation with lasers. Finally, spectroscopic aspects of lasers in medicine will be discussed. Applied aspects of laser spectroscopy have been covered in [10.1,2]. 

Perhaps the most marked difference between flame AAS and flame AFS is the fact that, in the latter technique, the signal increases with the useful source intensity. Source intensity (for a constant line profile) has no effect in AAS, because absorbance is a ratio (see Chapter 1). For this reason, over almost three decades a great deal of research effort has gone into trying to produce more intense and stable sources for use in AFS. For some elements, very low detection limits have been obtained using lasers as excitation sources. A comparison of detection limits by AFS using diverse sources may be found in the useful critical and comprehensive review of AFS by Omenetto and Winefordner.7 Such sources have found very limited application in routine environmental analysis, primarily because of cost and lack of standard commercially available instrumentation they will not be considered further here. 

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